Sometimes you just need to know if a MIDI controller is outputting anything. Even many high-end MIDI modules/boxes will have a “MIDI Activity” light, just to let you know something is being transmitted/received. That’s what I have made in this video.

Using a sacrificial MIDI cable, an LED, and a 220 Ohm resistor, you too can make this tester/activity light, probably in less than 10 minutes. Here is a rough wiring diagram.

There really isn’t too much critical about the parts used. MIDI devices use a 5 mA current loop at 31.25 Kbaud as part of their serial communication protocol. Most LEDs and a ~220 Ohm resistor will result very close in the neighborhood of 5 mA when used in this circuit. Devices with a MIDI input have basically this same thing as the LED, except in the form of an optoisolator IC.

I’ll be exploring MIDI much more in-depth in future videos. Let me know in the comments below if you have any ideas/questions for future videos about MIDI.

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